1. Field of the Invention
The present invention relates to a recording apparatus and recording method for performing recording on a prescribed recording medium on the basis of prescribed recording data for a plurality of pixels, by using a recording device which records dots by ejecting droplets of ink onto the recording medium.
2. Description of the Related Art
An inkjet recording apparatus has been known which ejects droplets of inks of mutually different colors on a prescribed recording medium, and an inkjet recording apparatus has also been known which ejects droplets of inks of mutually different droplet volumes onto a prescribed recording medium.
In the case of an image in which the same tonal graduation continues, cyclical density non-uniformities or streaks may appear on the recording medium, due to error in the ink depositing position, or error in the scanning accuracy (and more specifically, error in the feed accuracy of the recording medium, and error in the feed accuracy of the carriage of the recording head).
Furthermore, the occurrence of cyclical density non-uniformities or streaks is closely related to the coverage rate of the dots per unit surface area of the recording medium. In particular when images having low to medium tonal regions are recorded, if dots of mutually different sizes are recorded onto coinciding positions on the recording medium, then the effective dot coverage rate becomes low and density non-uniformities and streaks become readily visible.
Furthermore, if a plurality of dots of mutually different sizes or a plurality of dots of mutually different colors are recorded on the same positions on the recording medium in one scanning operation, then when observed locally, the ink is not absorbed completely into the recording medium, the dot shapes on the recording medium are disturbed, and an impression of undesirable “image noise” may occur in the formed image.
Japanese Patent Application Publication No. 2004-148723 discloses an inkjet recording apparatus which carries out recording on a recording medium, on the basis of recording data represented by a graduated tone value (the n value), using a recording device having first recording elements and second recording elements which record dots of mutually different sizes. The inkjet recording apparatus includes: a storage device which previously stores a plurality of dot patterns; a device which selects dot patterns corresponding to the respective graduated tone values of the recording data, from the plurality of dot patterns previously stored in the storage device; and a control device which performs recording by means of the first recording elements and the second recording elements, in accordance with the data in the buffer, wherein the storage device stores dot patterns in which the dot positions of the first recording elements and the second recording elements do not coincide.
An inkjet recording apparatus has been known which is able to eject very small droplets of approximately 1 picoliter (pl). Such a very small liquid droplet is typically accompanied by a satellite droplet (also referred to as a “sub-droplet” or “subsidiary droplet”) having substantially the same size as the main droplet. Therefore, when considering the dot arrangement, it is necessary to take account of the dot positions of the satellite droplets, as well as the dot positions of the main droplets.
Japanese Patent Application Publication No. 2004-148723 discloses a composition which uses dot patterns where the positions of two dots do not coincide, in order to improve the coverage rate per unit surface area, of small dots and large dots on the recording medium. However, in cases where satellite droplets have large effects, in other words, if the dot coverage rate per unit surface area, of the dots composed of satellite droplets deposited on the recording medium is close to the coverage rate per unit surface area, of the dots composed of main droplets deposited on the recording medium, then it is difficult to avoid density non-uniformities or disturbance of the dot shapes unless the satellite droplets are taken into account.
This problem is described here with reference to FIG. 18. In FIG. 18, a large dot pattern 91 for a first recording element which records a large dot onto the recording medium, and a small dot pattern 92 for a second recording element which records a small dot onto the recording medium, form a set of dot patterns in which the dot positions do not coincide with each other. However, in a synthesized dot pattern 95 obtained by combining the dot pattern 93 which indicates the position of the dot 93M actually recorded on the recording medium by the first recording element, and the dot pattern 94 which indicates the positions of the dots 94M and 94S actually recorded on the recording medium by the second recording element, there is coincidence in the dot positions on the recording medium between the dot 93M recorded by the main droplet ejected from the first recording element and the dot 94S recorded by the satellite droplet ejected from the second recording element.
The problem of coincidence between the dot position of a main droplet and the dot position of a satellite droplet as described above occurs similarly between inks of different colors.